Kinase inhibitors created a new paradigm in chemotherapy and are a major focus of new oncology drug development, but developmental success rates are low (5-10%). Resistance to kinase inhibitors occurs through target-dependent mechanisms (e.g. point mutations that abrogate drug binding) and target-independent mechanisms (e.g. upregulation of alternative signaling pathways, termed kinome reprogramming). Therefore, combinations of inhibitors that target several kinases at once are desirable to have a better chance of avoiding the resistance/relapse cycle. Detecting protein kinase activity inside living cells (rather than in lysates or reconstituted systems) is important for understanding kinase inhibitor drug sensitivity and resistance mechanisms, and would lead to better screening for inhibitors likely to make it through the development process. We will develop multiplexed, cell-based assays for specific kinase activities that are important to inhibitor response and kinome reprogramming, and use them to detect kinase activation profiles in patient cells and for inhibitor screens. Phosphorylation of the biosensors is detected using time-resolved lanthanide luminescence measurements, in which Tb3+ emission energy is measured directly via small molecule fluorophores to give different emission colors depending on the fluorophore. In Aim 1, we will establish quantitative assays for activity (and therefore inhibition) of key kinases in drug sensitive and drug resistant CML cells, profiling the pathway activation phenotypes in therapeutically relevant cellular states. We will use the set of biosensors we have already established in preliminary work, and add biosensors for other kinases as they are developed. The assays will be established with cell lines and samples from CML patients (comparing to healthy controls), and validated with RT-qPCR and SWATH proteomics. In Aim 2, we will screen for synergies between existing kinase inhibitor drugs and new compounds (via libraries). We will also develop homogenous multiplexed analysis of biosensor phosphorylation using energy transfer from lanthanides to organic dyes. In Aim 3, we expand the biosensor design pipeline to develop new, non-natural peptide substrates to use as biosensors for other kinases. The work described in this aim will add to the set of biosensors we already have available. Completion of the work described in this proposal will give us a novel assay for multiple kinases, a suite of new biosensors as well as new and refined detection strategies to use in screening. Drug discovery will benefit from this technology's ability to address kinome reprogramming mechanisms by targeting several kinases at a time. Drug development will benefit from companion assays for multiple targets that could follow a drug or drug combination through the hit to lead transition, target validation, pre-clinical studies, clinical trials, and beyond into treatment management. This assay and its associated tools will contribute to the next generation of targeted therapy development in cancer by breaking new ground in our ability to model the disease environment during drug screening and development.